You are right. Twitter integration is currently not working. We'll investigate the root cause. Thanks for the heads up.

Update 1 (2020-06-06): The fixed improved version is in progress.
Update 2 (2020-06-06): The new Twitter integration is now in testing and polishing. It not only restores the support but also makes it a lot better (will provide support for home, explore, user feeds, list feeds, hashtag feeds and search and does it more efficiently than before).
Update 3 (2020-06-08): the new Twitter integration is almost polished. It's going to be great. :)
Update 4 (2020-06-17): Twitter integration works great in our testing. Also other integrations were enhanced and lots of changes were made so extensive testing is required to ensure that there are no memory leaks or other nasty things. Releasing soon! Thanks for your patience.
Update 5 (2020-06-24): Feedbro 4.4.0 is now in the Mozilla Add-On Store review queue. It has the fixed & improved Twitter integration, significantly improved LinkedIn integration and a lot more! Hopefully becomes available soon.
Update 6 (2020-07-01): it's now available!